AUTHOR=Calabrese Silvia , Pérez-Tienda Jacob , Ellerbeck Matthias , Arnould Christine , Chatagnier Odile , Boller Thomas , Schüßler Arthur , Brachmann Andreas , Wipf Daniel , Ferrol Nuria , Courty Pierre-Emmanuel 

TITLE=GintAMT3 – a Low-Affinity Ammonium Transporter of the Arbuscular Mycorrhizal Rhizophagus irregularis

JOURNAL=Frontiers in Plant Science

VOLUME=7

YEAR=2016

URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2016.00679

DOI=10.3389/fpls.2016.00679

ISSN=1664-462X

ABSTRACT=<p>Nutrient acquisition and transfer are essential steps in the arbuscular mycorrhizal (AM) symbiosis, which is formed by the majority of land plants. Mineral nutrients are taken up by AM fungi from the soil and transferred to the plant partner. Within the cortical plant root cells the fungal hyphae form tree-like structures (arbuscules) where the nutrients are released to the plant-fungal interface, i.e., to the periarbuscular space, before being taken up by the plant. In exchange, the AM fungi receive carbohydrates from the plant host. Besides the well-studied uptake of phosphorus (P), the uptake and transfer of nitrogen (N) plays a crucial role in this mutualistic interaction. In the AM fungus <italic>Rhizophagus irregularis</italic> (formerly called <italic>Glomus intraradices</italic>), two ammonium transporters (AMT) were previously described, namely GintAMT1 and GintAMT2. Here, we report the identification and characterization of a newly identified <italic>R. irregularis</italic> AMT, GintAMT3. Phylogenetic analyses revealed high sequence similarity to previously identified AM fungal AMTs and a clear separation from other fungal AMTs. Topological analysis indicated GintAMT3 to be a membrane bound pore forming protein, and GFP tagging showed it to be highly expressed in the intraradical mycelium of a fully established AM symbiosis. Expression of GintAMT3 in yeast successfully complemented the yeast AMT triple deletion mutant (<italic>MAT</italic>a <italic>ura3 mep1</italic>Δ <italic>mep2</italic>Δ::<italic>LEU2 mep3</italic>Δ::<italic>KanMX2</italic>). GintAMT3 is characterized as a low affinity transport system with an apparent K<sub>m</sub> of 1.8 mM and a <italic>V</italic><sub>max</sub> of 240 nmol<sup>-1</sup> min<sup>-1</sup> 10<sup>8</sup> cells<sup>-1</sup>, which is regulated by substrate concentration and carbon supply.</p>